将32位十六进制加载到char数组中

Question

I am trying to load 32-bit hexadecimal into char array.

#define NUC 0xA8051701

unsigned char debug_msg[100];
sprintf (debug_msg, "%08x", NUC);

But it is loading only "A805" that to as ASCII character instead of hexadecimal. Can any one suggest what could be the problem.

What I'm actually looking for is:

debug_msg[0]=0xA8
debug_msg[1]=0x05
debug_msg[2]=0x17
debug_msg[3]=0x01

Instead of the correct value, it is loading as below:

debug_msg[0]=0x30
debug_msg[1]=0x30
debug_msg[2]=0x30
debug_msg[3]=0x30
debug_msg[4]=0x61
debug_msg[5]=0x38
debug_msg[6]=0x30
debug_msg[7]=0x35

Effectively it is loading 0x0000a805 that to in ASCII.

Answer 1

On the face of it, you need:

 debug_msg[0] = (NUC >> 24) & 0xFF;
 debug_msg[1] = (NUC >> 16) & 0xFF;
 debug_msg[2] = (NUC >>  8) & 0xFF;
 debug_msg[3] = (NUC >>  0) & 0xFF;

(where the >> 0 is optional but makes it look neater — if the compiler optimizes to omit any shift for that). If you want to handle different values in place of NUC , then:

unsigned long value = 0xA8051701;

debug_msg[0] = (value >> 24) & 0xFF;
debug_msg[1] = (value >> 16) & 0xFF;
debug_msg[2] = (value >>  8) & 0xFF;
debug_msg[3] = (value >>  0) & 0xFF;

Or in macro form:

#define MANGLE(value, debug_msg) \
    debug_msg[0] = (value >> 24) & 0xFF; \
    debug_msg[1] = (value >> 16) & 0xFF; \
    debug_msg[2] = (value >>  8) & 0xFF; \
    debug_msg[3] = (value >>  0) & 0xFF

used as:

MANGLE(0xA8051701, debug_msg)

or, if you want the values at arbitrary offsets in the array:

#define MANGLE(value, debug_msg, offset) \
    debug_msg[offset+0] = (value >> 24) & 0xFF; \
    debug_msg[offset+1] = (value >> 16) & 0xFF; \
    debug_msg[offset+2] = (value >>  8) & 0xFF; \
    debug_msg[offset+3] = (value >>  0) & 0xFF

Used as:

MANGLE(0xA8051701, debug_msg, 24);

There might be a need to wrap the body of the macro in a do { … } while (0) loop to make it work properly after an if statement, etc.

Or you could write an inline function to do the job. Or …

Answer 2

You can use a Union here

#define NUMBER_OF_BYTES_FOR_UINT    4
Union Char_UInt
{
  U8 u8data[NUMBER_OF_BYTES_FOR_UINT];
  U32 u32data;
};

Now, you can assign "NUC" (or any 32-bit number) to "u32data" and then read "u8data", It will give you byte-by-byte values.

This is because union assigns same memory to character array and u32data. You write and read from same memory location but through different interfaces.

Note that, Endianness of system plays a role here.